Lubricant composition containing a sulfide



United States Patent 3,274,107 LUBRICANT CONWOSITION CONTAINING A SULFIDE Glenn R. Wilson, Cambridge, Mass., Kenneth L. McHugh, Kirkwood, Mo., and John 0. Smith, Swampscott, Mass., assignors to Monsanto Research Corporation, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Apr. 30, 1963, Ser. No. 277,021

11 Claims. (Cl. 25246.4)

This invention relates to liquid fluids of high thermal stability, and more particularly, provides functional \fl'uids comprising polyphenyl ethers and certain aryl Group V element sulfides as additives therefor.

Polyphenyl ethers have found wide application as functional fluids owing to their very good thermal stability, lubricity, and resistance to foam. For example, they have been found to be valuable as hydraulic fluids, as heat-exchange media, as atomic reactor coolants, as diffusion pump fluids, as lubricants in motor operation generally, and particularly as jet engine lubricants.

As is known in the art, petroleum lubricants, in addition to the petroleum base stock, generally include additives which impart specific desired properties to the base stock, such as rust inhibitors, anti-oxidants, extreme pressure resisting agents, lubricity improvers, detersives and the like. The additives proposed heretofore have been designed to provide petroleum base compositions for lubrication in conventional equipment such as internal combustion engines of the automotive type, diesel engines and the like, in which the temperature of use is not excessive, not exceeding about 400 F. Advanced designs such as jet aircraft design have called for effective lubrication at higher temperatures, such as 500 F. and above, and for these designs, it was found that neither the petroleum base stock nor the conventional additives used therewith were practical. The temperatures of operation exceeded the boiling point of some lubricant composition components, and generally were in a range at which both lubricant and additives were thermally unstable and decomposed.

Development of synthetic base stocks like the polyphenyl ethers has provided lubricant fluids stable at temperatures above the useful range of the mineral oils. There is now a demand for compositions in which such functional fluids, with thermal stability superior to that of the mineral oils, are compounded with additives enhancing desirable properties thereof. Many materials known as useful mineral oil additives are, as stated, ex cluded from utility in this connection by volatility and lack of thermal stability at the temperatures of use of the polyphenyl ethers. Furthermore, it has been found that additives conventional in mineral oil lubricants do not perform predictably upon combination with synthetic base stocks. There are significant differences in chemical structure of the stocks which can affect the response to additives: for example, whereas the mineral oils consist of aliphatic hydrocarbons, the polyphenyl ethers are, by contrast, aromatic ethers. Indeed, base stocks chemically different from the mineral oils may actually suffer chemical attack by certain additives, with deleterious effects on their superior high temperature properties. Temperature of operation can also affect the performance of additives, and so forth. Thus an empirical approach has been required for the provision of improved lubricants including the polyphenyl ethers as base stocks.

One of the aspects in which the properties of the polyphenyl ether base stocks are considered deficient consists in their lubricity characteristics. The lubricity characteristics of a lubricant include its load-carrying abilities and its Wear properties. Compared to other syn- 3,274,107 Patented Sept. 20, 1966 ICC thetic high temperature lubricant fluids, the polyphenyl ethers rank high in lubricity characteristics. However, severe design requirements for applications such as aircraft engines include effective lubrication under high pressures as well as at high temperatures which the uncompounded polyphenyl ethers do not meet. Thus there is a demand for polyphenyl ether base compositions having improved lubricity properties.

Another aspect requiring attention in utilization of the polyphenyl ether base lubricants is oxidation stability. Although the polyphenyl ethers possess extremely good thermal stability, at temperatures of, say, over 550 F, they tend to deteriorate, not because of a decomposition reaction, but because at the higher temperatures they become quite readily oxidizable. The lubricity of the polyhenyl ethers is thereby impaired, since the oxidation products do not possess lubricating properties; moreover, the change in viscosity which is a consequence of the oxidation not only makes for inefficiency, but also may clog up the moving parts of the mechanism which the lubricant was originally intended to protect. Hence, the effect of additives on the oxidation stability of the polyphenyl ethers can be important, particularly when the polyphenyl ethers are to be used at the higher temperatures under conditions requiring exposure to air, where it is necessary to inhibit oxidation phenomena which the higher temperatures favor.

An object of the present invention is the provision of improved lubricant compositions employing polyphenyl ether fluids as base stocks.

A particular object of the present invention is to provide poly-phenyl ether base compositions having improved lubricity properties.

These and other objects will become evident upon consideration of the following specification and claims.

It has now been found that compositions consisting es sentially of an oxygenated carbonaceous base fluid comprising a polyphenyl ether and an additive amount of an aryl Group V element sulfide of the formula where Ar is an aryl radical, V is an element of Group V of the Periodic Table, X is a radical selected from the class consisting of aryl radicals and aliphatic hydrocarbon radicals, and Y is a radical selected from the class consisting of aryl radicals and chlorine radicals, have unusual ability to lubricate under ultra-high loads at high temperatures.

A general improvement in lubricity characteristics is achieved by addition of a compound of the stated kind to the polyphenyl ether base fluids, including both a decrease in wear and an increase in load-carrying ability. Moreover, a composition as provided by this invention is less oxidatively unstable than the base fluid.

To provide the lubricant compositions of this invention, the Group V compounds of the nature stated above are combined with a high temperature, oxygenated carbonaceous lubricant base fluid. This will be a base fluid of lubricating viscosity having a chemical structure made up of C, H and O, and characterized by thermal stability at temperatures up to at least about 500 F. In general, the lubricant compositions of this invention will be designed for lubrication of the moving parts of mechanisms operating in temperature ranges of 400 F. to 700 F. A particularly advantageous base fluid for use under these conditions comprises the above-mentioned polyphenyl ethers.

The polyphenyl ethers employed in the compositions of this invention have from 3 to 7 benzene rings and from 1 to 6 oxygen atoms, with the stated oxygen atoms joining the stated benzene rings in chains as ether linkages. One or more of the stated benzene rings in these polyphenyl ethers may be hydrocarbyl substituted. The hydrocarbyl substitutents, for thermal stability, must be free of CH and aliphatic CH, so that preferred aliphatic substituents are lower saturated hydrocarbon radicals (l to 6 carbon atoms) like methyl and tert-butyl, and pre ferred aromatic substituents are aryl radicals like phenyl, t-olyl, t-butylphenyl, and a-cumyl. In the latter case, the benzene ring supplied in the hydrocarbyl substituent contributes to the total number of benzene rings in the molecule. Polyphenyl ethers consisting exclusively of chains of from 3 to 7 benzene rings with at least one oxygen atom joining the stated benzene rings in the chains as an ether linkage have particularly desirable thermal stability.

Exemplary of the polyphenyl ethers containing aliphatic carbon which are suitable for high temperature base fluids are 3-ring polyphenyl ethers like l-(p-methyL phenoxy) 4 phenoxybenzene and 2,4 diphenoxy 1- methylbenzene, 4-ring polyphenyl ethers like bis[p-(prnethylphenoxy)phenyl] ether and bis[p-(p-tert-butylphenoxy)phenyl] ether, and so forth.

Polyphenyl ethers consisting exclusively of benzene rings and including ether oxygen atoms linking said rings are exemplified by the triphenoxy benzenes and arylsubstituted polyphenyl ethers such as biphenylyl phenoxyphenyl ether, biphenylyloxyphenyl phenoxyphenyl ether, biphenylyl ether, dibiphenylyloxybenzene, bis(biphenylyloxyphenyl) ether, and the like.

A preferred class of the polyphenyl ethers are those consisting of benzene rings joined in a chain by oxygen atoms as ether linkages between each ring, of the formula C H O--(C H O) C l-I where n is an integer of from 1 to 5.

Examples of the polyphenyl ethers contemplated in this class are the bis(phenoxyphenyl) ethers (4 benzene rings joined in a chain by 3 oxygen atoms), illustrative of which is bis(m-phenoxyphenyl) ether. The bis (phenoxyphenoxy) benzenes are particularly valuable in the present connection. Illustrative of these are m-bis(rnphenoxyphenoxy)benzene, m bis(p phenoxyphenoxy) benzene, o-bis(o-phenoxyphenoxy)benzene, and so forth. Further, the polyphenyl ethers contemplated herein include the bis(phenoxyphenoxyphenyl) ethers such as bis[rn-phenoxyphenoxy)phenyl] ether, bis[p-(p-phenoxyphenoxy)phenyl] ether, and m-(m-phenoxyphenoxy) phenyl m-(o-phenoxyphenoxy)phenyl ether and the bis(phenoxyphenoxyphenoxy)benzenes such as m-bis[m- 1 (m-phenoxyphenoxy)phenoxy] benzene, p bis[p (mphenoxyphenoxy)phenoxy] benzene and m :bis [m (pphenoxyphenoxy phenoxy] benzene.

The preferred polyphenyl ethers are those having all their ether linkages in the meta-positions since the allmeta-linked ethers are particularly advantageous because of their wide liquid range and high thermal stability. However, mixtures of the polyphenyl ethers, either isomeric mixtures or mixtures of homologous ethers, can also advantageously be used in some applications, especially Where particular properties such as lower solidification points are required. Mixtures of polyphenyl ethers in which the non-terminal phenylene rings are linked through oxygen atoms in the meta and para positions have been found to be particularly suitable to provide compositions with wide liquid ranges. Of the mixtures having only meta and para linkages a preferred polyphenyl ether mixture of this invention is the mixture of bis(phenoxyphenoxy)benzenes wherein the non-terminal phenylene rings are linked through oxygen atoms in the meta and para position, and composed by weight of about 65% m-bis(m-phenoxyphenoxy) benzene, 30% m-[ (m-phenoxyphenoxy) (p-phenoxyphenoxy) ]benzene and 5% m-bis(p-phenoxyphenoxy)benzene. Such a mixture solidifies at below room temperature (that is, below 70 F.) whereas the three components solidify individually at temperatures above normal room temperatures.

The aforesaid polyphenyl ethers can be obtained by known procedures such as, for example, by the Ullmann ether synthesis, by a procedure involving reaction of alkali metal phenoxides such as sodium and potassium phenoxides with aromatic halides such as bromobenzene in the presence of a catalyst such as metallic copper, copper hydroxides or copper salts.

The high temperature, oxygenated carbonaceous base fluids employed in the compositions of this invention may also comprise a synthetic ester base fluid. These are fluids of lubricating viscosity and thermally stable to at least about 400 R, which are esters of alcohols containing at least 4 carbon atoms and which generally contain more than one ester group. They may be esters of polyhydric alcohols, of polybasic acids, or both.

Ester fluids with particularly advantageous low temperature viscosity properties, which flow readily at temperatures as low as 30 F are provided by the diesters of dibasic acids. Ester lubricants of the dibasic acid ester type are illustrated by diesters of long chain dicarboxylic acids like azelaic acid with long-chain branched primary alcohols of the C to C range. The synthetic ester lubricants also frequently include the esters of long chain m-onobasic acids such as pelargonic acid with glycols such as polyethylene glycols. Complex esters are also formed by linking dibasic acid half esters through a glycol such as dipropylene glycol, a polyethylene glycol of 200 molecular weight, and so forth. Permutation and combination of these methods of forming polyester type lubricant fluids have been reported to be valuable and also, it is common practice to achieve desired properties in the ultimate base fluid by blending different polyester products. Simple esters providing suitable fluids can be exemplified, for example, by bis(Z-methylbutyl) sebacate, bis(l methyl-4-ethyloctyl) sebacate, bis(2ethylhexyl) sebacate, dipropylene glycol dipelargonate, the diesters of acids such as sebacic, azelaic and adipic acid with complex C -C primary branched chain alcohols such as those produced by the 0x0 process, polyethylene glycol 200 bis(Z-ethylhexyl sebacate), diisoamyl adipate, 1,6- hexamethylene glycol di(2 ethylhexanoate), bis(dimethylamyl) azelate and so forth.

Ester fluids with particularly good high temperature oxidation resistance are provided by neopentyl polyol esters. The alcohols from which these esters are derived have the carbon structure of neopentane, with a central carbon atom surrounded by 4 substituent carbon atoms. Included in the neopentyl polyols are neopentyl glycol, trimethylolethane, trimethylolpropane and pentaerythritol. Generally, the base fluids comprising neopentyl polyol esters are the esters with monocarboxylic acids. Such esters are generally more oxidatively and thermally stable than the dibasic acid esters. The useful esters of the neopentyl polyols include, for example, the esters of trimethylol propane, neopentyl glycol and pentaerythritol with normal, branched chain and mixed acids having chain lengths varying from C to C Thus, an illustrative series of esters are trimethylolpropane tri-n-pelargonate, trimethylolpropane tricaprate, trimethylolpropane tricaprylate, the trimethylolpropane triester of mixed octanoates, and the like.

For further description of still other ester fluids adapted for use as lubricant base stocks and useful in the provision of the blends of this invention, reference may be made, for example, to the discussion in Gunderson et al., Synthetic Lubricants (Reinhold, 1962).

The base fluid in the present compositions may consist essentially of a polyphenyl ether base fluid alone, or a combination of the polyphenyl ether with a synthetic ester base fluid. The polyphenyl ethers are not generally miscible with other base fluids: they do not dissolve more than about 5% by weight mineral oil, for example. Attempts to blend silicones with the phenyl ether base fluids have shown that only a few of this class of fluids are miscible with the polyphenyl ethers, and then to a limited extent. However, it has been found that the polyphenyl ethers can be combined with other oxygenated carbonaceous base fluids to provide homogenous fluids having advantageous properties.

A deficiency of the polyphenyl ether base fluids having exceptional thermal and oxidative stability, as exemplified by the -bis(phenoxyphenoxy)benzenes discussed above, is lack of fluidity at low temperatures. The fluid range of these materials is unusually wide, encompassing the range from below 100 F. to above 800 F. However, the pour point of certain of these particularly stable fluids is above F., whereas for lubricant use, for example, ability to flow down to temperature climate winter temperatures such as 0 F. is desirable. It has been found that compositions comprising combinations of ester base fluids and the polyphenyl ethers can be provided which have the desired fluidity at low temperatures.

The lubricant fluids which have been found to blend with the phenyl ethers of good thermal and oxidative stability include various esters. It is particularly desirable to provide blends having thermal and oxidative stability at least approaching the stability of the polyphenyl ethers. In this connection, especially valuable base fluids have been found to be provided by combinations of a polyphenyl ether with a neopentyl alcohol ester. These compositions possess both fluidity at low temperature and stability at elevated temperatures.

The preferred polyphenyl ethers for use in this connection are the bis(phenoxyphenoxy)benzenes, of the composition C H O-(C H O-) -C H where each C H is a phenyl and each C H is a phenylene radical. Those with the ether linkages between benzene rings in meta positions, partly or wholly, are especially preferred. The stated neopentyl esters are esters of neopentyl alcohols such as pentaerythritol, trimethylolethane, trimethylolpropane and neopentyl glycol with straight chain, branched chain and mixed C C acids such as n-heptanoic and neoheptanoic acid.

Compositions of the stated valuable nature are pro vided by combining 2575 weight percent of the ester base fluids with 7525 weight percent of the polyphenyl ethers.

Referring to the additives combined with the abovedescribed base fluids in accordance with this invention, these are aryl Group V element sulfides of the formula where Ar is an aryl radical, V is a Group V element, X is selected from aryl radicals and aliphatic hydrocarbon radicals, and Y is selected from aryl radicals and chlorine radicals. The Group V elements particularly contemplated in this connection are P and Sb. The term aryl is used here to designate radicals including a cyclic nucleus having the resonating bond system characteristic of the benzene nucleus and bonded by a ring carbon atom of said cyclic nucleus to the Group V element. The said radicals may be hydrocarbon or may include the elements 0, S and N as hetero atoms, as part of an aryl ring nucleus or, in the case of oxygen, as a linking ether group between aryl nuclei. Aliphatic hydrocarbon radicals in the stated compounds, for high temperature stability, must conform to the description stated above in connection with description of the alkyl polyphenyl ethers, that is, be free of CH and aliphatic CH. Thus the aliphatic substituents on the Group V element or on the stated aryl radicals should be lower saturated hydrocarbon radicals (1 to 6 carbon atoms) like methyl and tertbutyl.

Illustrative of the triarylphosphine sulfide presently contemplated are (for nomenclature, see C & E News, 30 (1952) 4515) triphenylphosphine sulfide, tritolylphosphine sulfide, trinaphthylphosphine sulfide, anthracyldiphenylphosphine sulfide, tripyridylphosphine sulfide, tripicolinylphosphine sulfide, tripyridazinylphosphine sulfide, tribenzofurylphosphine sulfide, tribenzothienylphosphine sulfide, tri-p-biphenylylphosphine sulfide, tris(phenoxyphenyl)phosphine sulfide, and the like.

The phosphine sulfides which contain mixed functions may be illustrated by dimethylphenylphosphine sulfide, methyldiphenylphosphine sulfide, t-butyldiphenylphosphine sulfide, bis(phenoxyphenyl)methylphosphine sulfide, methyldipyridylphosphine sulfide, diphenylphosphinothioic chloride, ditolylp'hosphinothioic chloride, phenylmethyh phosphinothioic chloride, phenyl-t-butylphosphinothioic chloride, methylnaphthylphosphinothioic chloride, methyl- (phenoxyphenyl) phosphinothioic chloride, methylpyridylphosphinot'hioic chloride, methylbiphenylylphosphinothioic chloride, t-butyl(phenoxyphenyl)phosphinothioic chloride, t-butylphenyl-2,3-mesitylphosphinothioic chloride and the like.

Further illustrating the presently contemplated additives are the corresponding compounds of antimony, includ ing, for example, (nomenclature paralleling above rules), triphenylstibine sulfide, tribiphenylylstibine sulfide, tris- (phenoxyphenyl)stibine sulfide, tripyridylstibine sulfide, tribenzofurylstibine sulfide, phenyldinaphthylstibine sulfide, methyldiphenylstibine sulfide, methyldibiphenylylstibine sulfide, t-butyldiphenylstibine sulfide, t-butyldibenzothienylstibine sulfide, phenylmethylstibinothioic chloride, t-butyltolylstibinothioic chloride, methylnaphthylstibinothioic chloride, methylbiphenylylstibinothioic chloride, methylpryridylstibinothioic chloride, methylqui" olinylstibinothioic chloride and the like The compounds employed in accordance with this invention as additives have a general lubricity-improving effect on the polyphenyl ether base fluids. The aryl phosphine sulfides are characterized particularly by wearreducing efiects which are most pronounced at higher temperatures, in the range where the polyphenyl ether base fluids are of particular value. This kind of compound also has unusually high solubility in the base fluid. The class of aryl phosphinothioic chlorides is especially characterized by beneficial effects on the general lubricity characteristics representing the combined effects of increase in load-carrying ability and decrease in Wear. The antimony compounds contemplated as additives herein have the unusual property of maintaining wear substantially constant at a low value throughout a broad temperature range, whereas the wear-reducing properties of active additives in the polyphenyl ether base fluids are generally temperature-dependent. Additionally, the presently employed antimony compounds are the preferred class for reducing susceptibility of the base fluids to oxidative degradation, and in this connection also, they maintain viscosity increase due to high temperature oxidation at a constant value, independent of the presence or absence of metallic surfaces, which affects and changes the oxidation stability of the additive-free fluid.

The aryl Group V element sulfide is combined with the polyphenyl ether base fluid to the extent of generally, between about 0.01% and 10% by weight of the fluid. Particular effective amounts depend on the nature of the individual additive and of the ether fluid. In most cases the ability of the agent with respect to extreme pressure lubrication improvement increases as the concentration is increased, whereas lowering the concentration sometimes enhances antioxidant effects. For purposes of supplying additive concentrates, adapted for convenient formulation of finished lubricant compositions, useful compositions may comprise up to about a 1:1 weight ratio of the additives of this invention and the polyphenyl ether base fluid.

It will be appreciated that the compositions of this invention, in addition to the polyphenyl ether base fluid and the aryl Group V element sulfide may additionally include any of a Wide variety of further additives. For example, these may include sludge inhibitors and detergents such as the oil-soluble petroleum sulfonates, to loosen and suspend products of decomposition and counteract their effect. Other agents such as viscosity index improvers, as exemplified by alkyl methacrylate polymers, pour point depressants, oiliness agents, and so fourth, may also be present in these compositions if desired.

The invention is illustrated but not limited by the following examples, in which the tests employed to determine the reported adjuvant effects of the additive compounds when employed with the polyphenyl ether lubricant base fluid are conducted as follows:

The antiwear and extreme pressure lubrication characteristics of the lubricant compositions are evaluated by means of the well known Shell 4-Ball Extreme Pressure Tester and the Shell 4-Ball Wear Machine, as described, for example, in the Lubrication Engineers Manual (US. Steel Corp., 1960). These testers include 4 balls of stainless steel arranged in the form of an equilateral tetrahedron. The three lower balls are held immovably clamped in a holder to form a cradle in which the fourth upper ball is caused to rotate at 1200-1800 r.p.m. about a vertical axis in contact with the three lower stationary balls. The contacting surfaces of the balls are immersed in the test fluid which is held in a cup surrounding the assembly. A modified cup and heater assembly is used to evaluate lubricants at elevated temperatures and provisions are made to permit high temperature testing under an inert atmosphere: see the The Study of Lubrication Using the 4-Ball Type Machine by R. G. Larsen, Lubrication Engineering, 1, 35-43, 59 (Aug. 1945).

For determination of the extreme pressure properties in the 4-Ball EP tester, the upper ball is rotated while the load is gradually increased by increments of 10 kg. until the balls are welded together in a 1-minute test period.

For measurement of wear in the wear machine, the upper ball is rotated under a load of 40 kg. for one hour at each of the temperatures for which wear scar diameters worn in the surface of the three lower stationary balls are reported.

Additionally, present compositions have been submitted to the Falex antiweld test: see the articles by V. A. Ryan in Lubrication Engineering, September 1946, and by S. Kyropoulos in Refiner Natural Gasoline Manufacturer, vol. 18, pages 32024 (1939), and Amer. Soc. Test. Matls. D2, Section V, Tech. K. A steel journal pin is rotated by a driving shaft at 290 rpm. in jaws (V- bearing steel blocks) through which a constantly increasing load is applied, with ratchet means maintaining contact with the journal pin as it wears down during the test while the assembly is immersed in the lubricant. The load at failure due either to seizure or to Wear at a rate faster than the load-increasing rate is recorded.

For determination of the antioxidant affect of the presently employed additives, air is bubbled through heated samples for 24 hours at a rate of 1 liter per hour of air, in the presence and absence of Fe, Cu, Al and Ag wires. The percent change in viscosity (at 100 F.) from before to after oxidation is an index of antioxidant activity.

Example 1 This example illustrates the improvement in lubricity characteristics obtained with the polyphenyl ethers by addition of an aryl phosphine sulfide thereto.

A lubricant composition is prepared by adding triphenylphosphine sulfide to a polyphenyl ether base fluid having the following composition:

65% m-bis(m-phenoxyphenoxy)benzene,

30% m-[ (m-phenoxyphenoxy) (p-phenoxyphenoxy) Jbenzene,

5% p-bis(p-phenoxyphenoxy)benzene,

in a proportion of 4 grams (g.) of the sulfide to 100 g. of the base fluid (a concentration of 4% by weight).

Employing the above-described Shell 4-ball tester, extreme pressure and antiwear characteristics of the lubricant composition including the additive, and of the base 8 fluid in the absence of the additive are determined. The results obtained are as follows:

Wear Sear Weld Diameter, mm. Point, kg.

With additive 240 1. 21 0. 93 Without additive 2. l2 3. 05

Example 2 Wear Scar Weld Diameter, mm. Point, kg.

With additive 270 1 l9 1. 07 Without additive 1.82 2. 92

Example 3 This example further illustrates properties of the compositions of the invention comprising an aryl phosphinethioic chloride.

The lubricant composition prepared by combining methylphenylphosphinothioic chloride with a polyphenyl ether base fluid as set forth in Example 2 is subjected to the Falex test, which is described above, whereby the combined effect of extreme pressure and antiwear properties is measured. The minimum test value on this machine is about 500, and the polyphenyl base fluid by itself usually gives values in the test of between 500 and 1000. The maximum possible reading on the machine is 4500. Employing the above-described composition, in duplicate runs, the readings obtained are about 4000.

Example 4 Weld Wear Scar Diameter, mm Point, kg.

167 F. 400 F. 600 F.

With additive 210 1. 07 1. 05 O. 80 Without additive 150 l. 82 1. 17 2. 92

Example 5 This example provides an illustration of the improved oxidation stability of compositions of this invention as compared to the base fluid in the absence of additive.

The additive-containing lubricant composition described in Example 4, containing 1% triphenylstibine sulfide, is subjected to the above-described oxidation-corrosion test,

conducted with and without the presence of Wires of Fe, Ag, Cu and Al. Whereas the polyphenyl ether base fluid without additives suffers a 45% increase in viscosity in the absence of the wires, and 60% in their presence, the composition including the antimony sulfide compound undergoes only about a 20% viscosity increase in the same length of time, and the presence or absence of the metals does not afiect its oxidation stability.

Example 6 This example illustrates compositions including the present additives and base stocks consisting of blends of a polyphenyl ether base fluid and a polyester base fluid.

A blended base stock having a pour point below F. is .prepared by combining a polyphenyl ether base stock consisting of the mixture of 'bis(phenoxyphenoxy)benzenes described in the above examples and a trimethylolpropane tri-n-heptanoate ester, in the ratio of 55% by weight of the polyphenyl ether to 45 of the ester base stock. This blend has a 100 F. viscosity of about 50 centistokes (cs.), which is approximately doubled by exposure to an air flow of one liter per hour for 24 hours at 500 F. in the presence of Al, Cu, Ag and Fe wires.

A composition prepared by combining this blend with triphenylstibine sulfide, in a ratio of 1.0 g. of the sulfide per 100 g. of the blend, undergoes only about a 40% increase in viscosity (initial 100 F. viscosity, 45 cs.; aftertest viscosity, 62 cs.) under the same conditions.

While the invention has been described with reference to specific preferred embodiments thereof, it is to be appreciated that modifications and variations can be made Without departing from the scope of the invention, which is limited only as defined in the appended claims.

What is claimed is:

1. A lubricant composition consisting essentially of a base fluid comprising a polyphenyl ether and an adjuvant amount of a lubricity improving compound, said polyphenyl ether containing from 3 to 7 benzene rings joined by oxygen as ether linkages and said compound being an aryl Group V element sulfide of the formula where Ar is an aryl radical, V' is an element selected from the group consisting of phosphorus and antimony, X is a radical selected from the class consisting of aryl and aliphatic hydrocarbon radicals, and Y is a radical selected from the class consisting of aryl hydrocarbon radicals and chlorine radicals.

2. The composition of claim 1 in which the base fluid contains an ester blended with the polyphenyl ether, said ester being selected from the class consisting of diesters of alkanoic acids of from 4 to 14 carbon atoms with alkanols of from 4 to 12 carbon atoms; diesters of alkanoic acids of from 4 to 14 carbon atoms with polyalkylene glycols of molecular weight up to 200 in which the alkylene group has from 2 to 3 carbon atoms; and esters of mopentyl polyols with alkanoic acids of from 6 to 12 carbon atoms.

3. The composition of claim 1 wherein the Group V element of said aryl Group V element sulfiide is phosphorus.

4. The composition of claim 3 wherein said phosphorus sulfide is an aryl phosphine sulfide.

5. The composition of claim 4 wherein said aryl phosphine sulfide is triphenylphosphine sulfide.

6. The composition of claim 3 wherein said phosphorus sulfide is an aryl phosphinothioic chloride.

7. The composition of claim 6 wherein said aryl phosphinothioic chloride is methylphenylphosphinothioic chloride.

8. The composition of claim 1 wherein the Group V element of said aryl Group V element sulfide is antimony.

9. The composition of claim 8 wherein said antimony sulfide is an aryl stibine sulfide,

10. The composition of claim 9 wherein said aryl s-tibine sulfide is triphenylstibine sulfide.

11. The composition of claim 1 in which the base fluid consists essentially of a poylphenyl ether.

References Cited by the Examiner UNITED STATES PATENTS 2,138,835 12/1938 Butz 252466 2,993,929 7/1961 Rattenbury 260 543 3,169,925 2/1965 Mahoney 25249.8

DANIEL E. WYMAN, Primary Examiner.

I. MCBRIDE, L. G. XIARHOS, Assistant Examiners, 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A BASE FLUID COMPRISING A POLYPHENYL ETHER AND AN ADJUVANT AMOUNT OF A LUBRICITY IMPROVING COMPOUND, SAID POLYPHENYL ETHER CONTAINING FROM 3 TO 7 BENZENE RINGS JOINED BY OXYGEN AS ETHER LINKAGES AND SAID COMPOUND BEING AN ARYL GROUP V ELEMENT SULFIDE OF THE FORMULA 